Hello jules: I noticed this is your first post here on PC. So... welcome to PsychCentral.

I'm sorry I cannot be of help with regard to the tragic situation you describe. Hopefully there will be other members, here on PC, who will have some suggestions they can share. In the meantime, here are links to 5 articles, from PsychCentral's archives, that hopefully may be of some help:

Children and Grief

Children Dealing with Grief

Teaching Children the Skill of Grieving

Talking to Your Child About the Loss of a Loved One, Part 4

Parenting after Traumatic Events: Ways to Support Children

I hope you find PC to be of benefit.